Airbag door with an electromagnetic field

ABSTRACT

An airbag deployment safety device ( 25 ) is provided comprising a first conductive path ( 48   a ) for receiving an input signal, a second conductive path ( 48   b ) for receiving an induced signal through electromagnetic coupling of the first conductive path ( 48   a ) and the second conductive path ( 48   b ), and a processor circuit ( 79 ) configured to control deployment of the airbag ( 25   a ) in response to a comparison of the induced signal to a predetermined path.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a National Stage of International Application No.PCT/US01/07314 filed Mar. 7, 2001, which designated the United States,(International Publication No.: WO 01/66386) and claims benefit of U.S.provisional patent application Ser. No. 60/187,529 filed on Mar. 7,2000.

This invention relates generally to airbag doors and, more particularly,to airbag doors which make use of an electromagnetic field thereonfunctioning as a safety device in controlling airbag deployment.

Whereas thousands of lives have been saved by airbags, a large number ofvehicle occupants have also been injured, some seriously, by deployingairbags. For a variety of reasons vehicle occupants may be too close tothe airbag before it deploys and can be seriously injured or killed as aresult of the deployment thereof.

In response, so called “out-of-position” occupant sensors have beendeveloped is to determine the location of the head and/or chest of thevehicle occupant relative to the airbag based on the presumption it isthe impact of either the head or chest with the deploying airbag whichcan result in serious injuries.

While the impact of a vehicle occupant's head or chest with a deployingairbag may result in serious injuries, equally serious injuries mayresult from a vehicle occupant's contact with the airbag deployment dooror objects located thereon which may be transformed into projectilesupon deployment. In such an instance, the so called “out-of-position”occupant sensors which sense the location of the vehicle occupant's headand/or chest may offer no benefit to a correctly positioned occupant.

For example, some vehicle occupants while in proper position for airbagdeployment, rest their feet on the instrument panel, often directly onthe airbag deployment door. Still other vehicle occupants, also inproper position for airbag deployment, place objects such as books,coffee cups, pens, sunglasses, cigarettes, keys, documents, soda cans,palm computers, portable CD-players, portable phones, radar detectorsand other similar items directly on the airbag deployment door.

In light of the forgoing disadvantages of out-of-position sensors, whatis needed is an airbag deployment safety device which can detect foreignobjects (i.e. items not provided by the vehicle manufacturer at the timeof vehicle manufacture) located on and around an air bag deployment doorand, in response to the presence of such objects, temporarily disarm theairbag system. Then, once the objects are removed, the airbag deploymentsafety device can rearm the airbag system, making it again ready foruse.

An airbag deployment safety device is provided comprising a firstconductive path for receiving an input signal, a second conductive pathfor receiving an induced signal through electromagnetic coupling of thefirst conductive path and the second conductive path, and a processorcircuit configured to control deployment of the airbag in response to acomparison of the induced signal to a predetermined signal. By the term“control deployment” of the airbag, it is meant that the processorcircuit will either permit or prevent airbag deployment when otherwiseinitiated by an external triggering event.

According to another aspect of the invention, a method of triggering thedeployment of an airbag is provided comprising receiving an input signalto a first conductive path, receiving an induced signal to a secondconductive path through electromagnetic coupling of the first conductivepath and the second conductive path, comparing the induced signal with apredetermined signal, and controlling deployment of the airbag inresponse to the comparison of the induced signal to the predeterminedsignal.

According to another aspect of the invention, in the method ofcontrolling the deployment of an airbag, the predetermined signalcomprises a range of predetermined signals having an upper limit and alower limit and the step of controlling deployment of the airbag inresponse to the comparison of the induced signal to the predeterminedsignal further comprises permitting deployment of the airbag in responseto the comparison of the induced signal to the predetermined signal whenthe induced signal is within the range of predetermined signals and notpermitting deployment of the airbag in response to the comparison of theinduced signal to the predetermined signal when the induced signal isoutside the range of predetermined signals.

According to another aspect of the invention, a trim panel for a motorvehicle is provided comprising a first conductive path for receiving aninput signal, a second conductive path for receiving an induced signalthrough electromagnetic coupling of the first conductive path and thesecond conductive path, and an airbag deployment door.

According to another aspect of the invention, an airbag deployment dooris provided comprising at least a portion of one of a first conductivepath and a second conductive path, the first conductive path forreceiving an input signal and the second conductive path for receivingan induced signal through electromagnetic coupling of the firstconductive path and the second conductive path.

According to another aspect of the invention, an airbag deployment doorhaving an outer surface is provided, an electromagnetic field overlyingat least a portion of the outer surface of the airbag deployment door,the electromagnetic field configured to trigger deployment of an airbag.

To better understand and appreciate the invention, refer to thefollowing detailed description in connection with the accompanyingdrawings:

FIG. 1 is a perspective view of an airbag door system according to afirst embodiment of the present invention;

FIG. 2 is a perspective view of an airbag door system according to asecond embodiment of the present invention;

FIG. 3 is a cross sectional view of the airbag door system of FIG. 1taken along section line 3—3;

FIG. 4 is a perspective view of an airbag door system according to athird embodiment of the present invention;

FIG. 5 is a cross sectional view of the airbag door system of FIG. 4taken along section line 5—5;

FIG. 6 is a cross sectional view of an airbag door system according to afourth embodiment of the present invention taken along section line 5—5of FIG. 4; and

FIG. 7 is a cross sectional view of an airbag door system according to afifth embodiment of the present invention taken along section line 5—5of FIG. 4.

An exemplary airbag door system is shown at 25 in FIG. 1 comprising anairbag door 27 and trim panel 14. As shown in FIG. 3, airbag door system25 also comprises an air bag 25 a that is inflated by a gas generator 25b in response to a signal from a controller 25 c of a collision sensingdevice 25 d as is well known in the art. While illustrated with aninstrument panel, the airbag door system 25 can be employed as part ofany trim panel in the vehicle. For example, it can be part of sidepanels (e.g. door panels, quarter panels), headliners, overheadconsoles, floor consoles, package trays, parcel shelves, close-outpanels, seats, pillars, or any other part of a vehicle interior.

As shown in FIG. 3, the airbag door system 25 comprises a substratelayer 22, a foam layer 24, and a skin layer 26. The outer surface 18 ofskin layer 26 is the surface generally viewed by vehicle occupants.Generally, foam layer 24 is bonded directly to outer surface 23 ofsubstrate layer 22 and to inner surface 28 of skin layer 26.

Preferably, the outer surface 18 of skin layer 26 of trim panel. 14 iscontinuous across the boundary 29 defining airbag door 27. Alsopreferably, airbag door 27 is concealed from view by vehicle occupantsprior to deployment by the non-existence of any definitive seam, stylingline, gap, or other interruptions between the outer surface 18 of theairbag door 27 and trim panel 14 across boundary 29 which would indicatethe airbag door's presence. It is recognized that where airbag door 27is concealed prior to airbag deployment, the boundary 29 defining airbagdoor 27 from trim panel 14 may be difficult to ascertain, thusnecessitating airbag deployment to establish the boundary 29 as thelocation of separation between airbag door 27 and trim panel 14 uponairbag deployment.

As best shown in FIG. 3, a first conductor 66 of wire 48 a is preferablylocated within the confines of airbag door 27 while a second conductor68 of wire 48 b is preferably located within the confines of trim panel14. However, alternatively, both first conductor 66 of wire 48 a andsecond conductor 68 of wire 48 b may be located within the confines ofairbag door 27 or trim panel 14.

As best shown in FIG. 1, preferably both wires 48 a and 48 b (and thusfirst conductor 66 and second conductor 68) remain laterally displacedand substantially parallel to one another along at least a portion oftheir respective lengths. Also as shown, at least a portion of firstconductor 66 of wire 48 a and/or second conductor 68 of wire 48 b areadjacent boundary 29 defining airbag door 27. Also as shown, boundary 29defining airbag door 27 exists between and separates at least a portionof first conductor 66 of wire 48 a from second conductor 68 of wire 48b.

First conductor 66 and second conductor 68 comprise two electricallyconductive circuits. More particularly, as shown in FIG. 1, firstconductor 66 and second conductor 68 comprise input circuit 31 andoutput circuit 33, respectively. However, the relative location of eachcircuit is interchangeable and may be reversed. In other words, firstconductor 66 may comprise output circuit 33 and second conductor 68 maycomprise input circuit 31.

Input circuit 31 is provided with energy from a power source and, morepreferably, a device providing alternating or pulsating current and,even more preferably, an oscillator. Input circuit 31 and output circuit33 are electromagnetically coupled (i.e. a coupling which exists betweencircuits or conductors when they are mutually affected by the sameelectromagnetic field) prior to airbag deployment. More specifically,alternating current created in input circuit 31 generates acorresponding electromagnetic field around input circuit 31 in a mannerknown in the art.

As a result of being electromagnetically coupled, the electromagneticfield generated around input circuit 31 induces an electric current inoutput circuit 33. Data concerning the induced current (e.g. amperage)in output circuit 33 from input circuit 31 may be sensed by amicroprocessor 79. In order to establish initial threshold conditionsfor airbag deployment, data sensed by microprocessor 79 concerning theinduced current in output circuit 31 is preferably collected when airbagsystem 25 and electromagnetically coupled input circuit 31 and outputcircuit 33 are in a steady state (i.e. the condition in which circuitvalues remain essentially constant, after initial transients orfluctuating conditions have disappeared). Once the initial dataconcerning the induced current is collected, the data may be thenpreferably analyzed to establish a reference residual electric currentwith upper and lower threshold limits when airbag door system 25 may besafely deployed.

In operation, generally any physical object intruding into theelectromagnetic field encompassing input circuit 31 and output circuit33 will change the magnitude of the electromagnetic coupling and thusthe induced current in output circuit 33 from input circuit 31. As aresult, when the changed induced current is measured outside thepreviously established upper and lower threshold limits for thereference induced current, airbag door system 25 will not deploy. Thus,for example, when installed in a vehicle airbag door system 25 will notdeploy when a vehicle occupant or object (e.g. child, car seat, grocerybag) has intruded into the electromagnetic field generated around inputcircuit 31, resulting in a change in the electromagnetic coupling withoutput circuit 33, and a corresponding change in the residual electriccurrent measured outside the previously established upper and lowerthreshold limits of the reference residual electric current.

In addition to the vehicle use, the above structure may be used as aninspection device in the manufacturing facility for airbag door system25 to reduce, and preferably eliminate, the possibility of unintendedmanufacturing items (e.g. trim waste, rivet shanks, loose screws, etc.)from intruding into the electromagnetic field during manufacture andremaining undiscovered, thus posing a risk of becoming projectilesduring airbag deployment.

While the above embodiment provides an electromagnetic field whichoverlies at least a portion of the outer surface 18 of airbag door 27,and more particularly an electromagnetic field adjacent boundary 29defining airbag door 27, other variations may provide an electromagneticfield overlying an even greater portion (e.g. greater than 50%) ofairbag door 27.

In a second embodiment as illustrated in FIG. 2, where both firstconductor 66 of wire 48 a and second conductor 68 of wire 48 b arelocated within airbag door 27, the conductors may comprise asubstantially serpentine pattern 73 or other pattern which covers theouter surface 18 of airbag door 27 such that the electromagnetic fieldgenerated by input circuit 31 substantially overlies, and preferablycompletely overlies, the outer surface 18 of airbag door 27. In thismanner, generally any physical object intruding into the electromagneticfield overlying outer surface 18 of skin layer 26 will be detected asdescribed above and, under certain conditions, airbag door system 25will not deploy.

As can best be seen from FIG. 3, conductors 66 and 68 preferably arerectangular. More particularly, conductors 66 and 68 comprise anelectrically conductive metal, such as copper or similar metal, in theform of a thin foil, which are preferably insulated by insulator 70. Theuse of one or more conductors with a rectangular shape insulated by aninsulator may be referred to as “flat” wire. The use of flat wire, asopposed to traditional round wire with a round conductor, is preferredfor attachment to the outer surface 23 of substrate 22. However, bothflat and round wire may be used. More particularly, the flat wire 48 a,48 b may take the form of a flexible printed circuit (FPC).

Preferably wires 48 a, 48 b are at least partially surrounded by and,more preferably, at least partially embedded in the foam layer 24. Priorto being at least partially surrounded and embedded by the foam layer24, wires 48 a, 48 b may also be joined to the inner surface 28 of skinlayer 26 or to the outer surface 23 of substrate layer 22, but it isrecognized that wires 48 a, 48 b may be positioned at any locationtherebetween. More preferably, wires 48 a, 48 b are joined to the outersurface 23 of substrate layer 22 by a double-sided pressure sensitiveadhesive tape located therebetween or with mechanical fasteners (e.g.clips, screws, etc.).

In order to at least partially surround and embed wires 48 a, 48 b infoam layer 24, the wires 48 a, 48 b are preferably placed between theinner surface 28 of the skin layer 26 and the outer surface 23 ofsubstrate layer 22 prior to the introduction of the foam layer 24. Then,foam layer 24 is preferably formed by introducing a foam, or morepreferably, a foam precursor material between the inner surface 28 ofskin layer 26 and the outer surface 23 of substrate layer 22.Preferably, the foam precursor is a urethane foam precursor which isintroduced using a reaction injection molding process as known in theart. After the urethane foam precursor is introduced, the reactiveconstituents, a polyol and an isocyanate, begin to react, and thesubsequently created foam material formed between the inner surface 28of skin layer 26 and the outer surface 23 of substrate layer 22 bondsskin layer 26 to substrate layer 22 while at the same time flowingaround and preferably bonding to the exposed surfaces of wires 48 a, 48b.

Alternatively, wires 48 a, 48 b may be located in the skin layer 26. Forexample, the wires 48 a, 48 b may be at least partially surrounded byand, more preferably, at least partially embedded in the skin layer 26.Also, in the various embodiments, many types of adhesives, includingurethanes, etc., may be used to bond wires 48 a, 48 b to skin layer 26or substrate 22 of trim panel 14. The adhesives may be applied in anyone of a number of forms to include pressure-sensitive backings, hotmelts and spray coatings.

While skin layer 26 is preferably formed by casting, skin layer 26 mayalso be formed by spray coating, blow molding, or thermoformed sheet andthen incorporated into the subsequent foam forming process identifiedabove. With regards to more specific skin materials, skin layer 26 maycomprise thermoplastic or thermoset polymers. The group of thermoplasticpolymers includes, but is not limited to, polyvinyl chloride (PVC),thermoplastic urethane (TPU), and thermoplastic olefin (TPO). The groupof thermoset polymers includes, but is not limited to, polyurethane.

While foam layer 24 is preferably joined to skin layer 26 and substratelayer 22 simultaneously by the reaction injection molding process, foamlayer 24 may also be joined to skin layer 26 prior to introduction ofsubstrate layer 22 rather than simultaneously as identified above. Forexample, skin layer 26 and foam layer 24 may be provided as amulti-layer sheet which is subsequently heated and vacuum formed oversubstrate layer 22.

In a third embodiment of the invention as shown in FIGS. 4 and 5, skinlayer 26 comprises an airbag door skin portion 35 and a trim panel skinportion 37. Airbag door skin portion 35 comprises an electricallyconductive member and more preferably an electrically conductivepolymer. In this manner, airbag door skin portion 35 functions as afirst conductor 66 a and preferably, when connected to first conductor66 of wire 48 a, comprises an input circuit 31 which functions asdiscussed in the first embodiment. As for trim panel skin portion 37, itpreferably comprises a polymer with a lower electrical conductivity thanthe electrically conductive member of the airbag door skin to insulatethe electrically conductive member from short circuit.

With respect to preferred electrically conductive polymers, suchpolymers include, but are not limited to polymers that are electricallyconductive, e.g. those polymers that contain extended sequences ofconjugation, resulting in optimum resonance, which in the presence ofmetallic or metalloid ions, provide conductivity. Alternatively,electrically conductive polymers herein include polymers containingappropriate loadings of electrical conductor additive, such as metalpowders and/or metallic fibers. Along such lines, carbon, silver,graphite, mercury, aluminum, and copper filler are herein contemplated.

Also as part of the third embodiment, substrate layer 22 comprises anairbag door substrate portion 49 and a trim panel substrate portion 51.Preferably airbag door substrate portion 49 comprises an electricallyconductive member and more preferably an electrically conductive metalcoating or foil 77 applied to outer surface 23 of substrate 49.Preferably, the substrate layer 22 to which the electrically conductivemember is attached comprises a polymer with a lower electricalconductivity than the electrically conductive member to insulate theelectrically conductive member from short circuit. In this manner,airbag door substrate portion 49 functions as a second conductor 68 aand preferably, when connected to second conductor 68 of wire 48 b,comprises an output circuit 33 which functions as discussed in the firstembodiment. However, alternatively, any vehicle member comprising anelectrically conductive circuit displaced from and electrically coupledwith circuit 31 of airbag door skin portion 35 may be acceptable as aoutput circuit 33.

The two skin portions 35, 37 may be joined together by a plastic bond39. The bonding 39 may be formed by partially or completely overlappingand melt fusing the skin portions 35, 37 together, or may comprise aseparate material joined to each skin portion 35, 37 as explained ingreater detail below.

The airbag door skin and trim panel portions 35, 37 may be formedsimultaneously in a single forming process, such as casting using anelectroformed shell tool in a manner known in the art. As seen in FIGS.4 and 5, the airbag door skin portion 35 and trim panel portion 37 arepreferably cast with closely adjacent outer and inner edges 45 and 43,respectively, for the formation of the bond 39. The outer edge 45defines the periphery of the air bag door skin portion 35 and the inneredge 43 defines the periphery of trim panel skin portion 37 adjacent theair bag door skin portion 35 with bond 39 therebetween. An example of asimilar process of manufacture is disclosed in U.S. Pat. No. 5,863,064assigned to the assignee of the present invention and incorporated byreference.

Airbag door skin portion 35 may also include a tear seam 47 includedtherein in a manner known in the art to help facilitate airbagdeployment. However, while bond 39 and tear seam 47 are shown asseparate features, in other embodiments at least a portion of bond 39and tear seam 47 may be one and the same. According to such analternative embodiment, the composition of the bonding material used forthe bond 39 that joins skin portions 35 and 37 would be of a relativelyweaker (e.g. lower tensile strength) material. An example of this weakermaterial is disclosed in U.S. Pat. No. 5,288,103 assigned to theassignee of the present invention and incorporated by reference. Thelocation of bond 39 and/or tear seam 47 may be concealed from view byvehicle occupants by applying an outer coating 75 of paint to the outersurface 18 of skin layer 26.

In a fourth embodiment of the invention as shown in FIG. 6, a separatematerial for bond 39 is not required. In this embodiment, instead offorming airbag door skin portion 35 and trim panel skin portion 37simultaneously, airbag door skin portion 35 and trim panel skin portion37 are formed sequentially. For example, trim panel skin portion 37 maybe formed, such as by casting, before forming the air bag door skinportion 35. Then, in a subsequent forming operation, airbag door skinportion 35 may be formed, such as by casting. During the subsequentforming operation, trim panel skin portion 37 may be either partially orcompletely underlined with material from the subsequent forming cycle.

In a fifth embodiment of the invention as shown in FIG. 7, the higherelectrically conductive member used for airbag door skin portion 35 maybe covered from view and touch from vehicle occupants by the polymerused for trim panel skin portion 37. According to this embodiment,airbag door skin portion 35 and trim panel skin portion 37 are bothfirst formed as a first skin layer, preferably from casting, the polymerwith the lower electrical conductivity. Then, subsequent to theformation of the first skin layer, at least a portion of airbag doorskin portion 35 of the first skin layer is underlined with a higherelectrically conductive polymer. In this manner the lower electricallyconductive polymer functions as an insulator relative to the higherelectrically conductive polymer, both around and overlying.

We intend the above description to illustrate embodiments of the presentinvention by using descriptive rather than limiting words. Obviously,there are many ways that one might modify these embodiments whileremaining within the scope of the claims. In other words, there are manyother ways that one may practice the present invention without exceedingthe scope of the claims herein.

I claim:
 1. An airbag deployment safety device comprising: a firstconductive path for receiving an input signal; a second conductive pathfor receiving an induced signal through electromagnetic coupling of thefirst conductive path and the second conductive path; and a processorcircuit configured to control deployment of an airbag in response to acomparison of the induced signal to a predetermined signal, and anairbag deployment door, wherein at least a portion of one of the firstconductive path and the second conductive path are located on the airbagdeployment door.
 2. The airbag deployment safety device of claim 1wherein at least a portion of one of the first conductive path and thesecond conductive path are located on a trim panel.
 3. The airbagdeployment safety device of claim 2 wherein the trim panel comprises asubstrate; and at least a portion of one of the first conductive pathand the second conductive path are located on the substrate.
 4. Theairbag deployment safety device of claim 3 wherein the trim panelfurther comprises a skin at least partially covering the substrate; andat least a portion of one of the first conductive path and the secondconductive path are located on either the skin or the substrate, or at alocation in between.
 5. The airbag deployment safety device of claim 4wherein the trim panel further comprises a foam located between the skinand the substrate; and at least a portion of one of the first conductivepath and the second conductive path are at least partially surrounded bythe foam.
 6. The airbag deployment safety device of claim 2 wherein thetrim panel comprises a skin; and at least a portion of one of the firstconductive path and the second conductive path are located in the skin.7. The airbag deployment safety device of claim 2 wherein the trim panelcomprises a skin; and the skin comprises at least a portion of one ofthe first conductive path and the second conductive path.
 8. The airbagdeployment safety device of claim 7 wherein the skin comprises at leasta portion of the first conductive path and the second conductive pathcomprises an electrically conductive polymer.
 9. The airbag deploymentsafety device of claim 2 wherein the trim panel comprises a substrate;and the substrate comprises at least a portion of one of the firstconductive path and the second conductive path.
 10. The airbagdeployment safety device of claim 2 wherein the trim panel comprises aninstrument panel.
 11. The airbag deployment safety device of claim 1wherein at least a portion of the first conductive path and secondconductive path are laterally displaced and substantially parallel toone another along at least a portion of their respective lengths. 12.The airbag deployment safety device of claim 1 wherein at least aportion of one of the first conductive path and the second conductivepath are adjacent a boundary of an airbag deployment door.
 13. Theairbag deployment safety device of claim 1 wherein at least a portion ofthe first conductive path and second conductive path are separated by aboundary of an airbag deployment door.
 14. The airbag deployment safetydevice of claim 1 wherein at least a portion of one of the firstconductive path and the second conductive path form a serpentinepattern.
 15. The airbag deployment safety device of claim 1 wherein atleast a portion of one of the first conductive path and the secondconductive path comprise a flat conductor.
 16. The airbag deploymentsafety device of claim 1 wherein at least a portion of one of the firstconductive path and the second conductive path comprise a flexibleprinted circuit.
 17. A method of controlling the deployment of an airbagcomprising: providing an input signal to a first conductive path;receiving an induced signal at a second conductive path throughelectromagnetic coupling of the first conductive path and the secondconductive path; providing a processor circuit configured to controldeployment of an airbag in response to a comparison of the inducedsignal to a predetermined signal; comparing the induced signal with apredetermined signal; and controlling deployment of the airbag inresponse to the comparison of the induced signal to the predeterminedsignal.
 18. The method of claim 17 wherein: the predetermined signalcomprises a range of predetermined signals having an upper limit and alower limit; and the step of controlling deployment of the airbag inresponse to the comparison of the induced signal to the predeterminedsignal further comprises: permitting deployment of the airbag inresponse to the comparison of the induced signal to the predeterminedsignal when the induced signal is within the range of predeterminedsignals; and preventing deployment of the airbag in response to thecomparison of the induced signal to the predetermined signal when theinduced signal is outside the range of predetermined signals.
 19. Themethod of claim 17 wherein at least a portion of one of the firstconductive path and the second conductive path are located on an airbagdeployment door.
 20. The method of claim 17 wherein at least a portionof one of the first conductive path and the second conductive path arelocated on a trim panel.
 21. The method of claim 20 wherein the trimpanel comprises an instrument panel.
 22. The method of claim 20 whereinthe trim panel comprises an air bag deployment door.
 23. The method ofclaim 17 an electromagnetic field overlies at least a portion of anouter surface of an airbag deployment door.
 24. A trim panel for a motorvehicle comprising: a first conductive path for receiving an inputsignal; a second conductive path for receiving an induced signal throughelectromagnetic coupling of the first conductive path and the secondconductive path; and an airbag deployment door.
 25. An airbag deploymentdoor comprising: at least a portion of one of a first conductive pathand a second conductive path, the first conductive path for receiving aninput signal and the second conductive path for receiving an inducedsignal through electromagnetic coupling of the first conductive path andthe second conductive path.
 26. An airbag deployment door having anouter surface, an electromagnetic field overlying at least a portion ofthe outer surface of the airbag deployment door, the electromagneticfield configured to control deployment of an airbag.